This invention relates to the monitoring of a physical property of a material, such as the specific gravity (density) of a manufactured meat product or the density, and hence weight, of tobacco in a xe2x80x9ccigarette rodxe2x80x9d of constant cross-sectional area, using a penetrative or diffractive radiation, for example an X-ray beam, and measuring its absorption by the material whose physical property is to be measured, to determine such property.
The invention has particular application in the meat processing industry, as well as other product processing industries, for example, the tobacco, pharmaceutical and plastics processing industries.
Typically, a material of which a physical property, such as the specific gravity, is to be monitored, is placed in the path of a beam of radiation, for example, an X-ray beam, to produce a signal at a sensor or an array of sensors representative of the value of the physical property which is dependent upon the amount of radiation absorbed by the product and, hence, the residual amount of radiation received by the sensor(s).
In the meat processing industry, the monitoring of the specific gravity of a meat product slurry or emulsion of various particle sizes can be used to determine changes in the proportion of fat within the product. Because the difference in specific gravities gives rise to only a very small signal variation using conventional techniques, it has been found necessary to develop a technique for monitoring the specific gravity of processed meat products to a greater accuracy than previously.
In the tobacco industry, weight control of cigarettes has been determined traditionally by monitoring the beta ray absorption of the cigarette at the point where it has been formed into a xe2x80x9crodxe2x80x9d. This technique forms part of a closed loop system for maintaining consistency in the weight of the cigarettes, which is particularly important in view of the high cost of tobacco products. At present, the application of radioactive sources, such as that for generating beta rays, is becoming increasingly undesirable due to the regulatory considerations associated with the handling and disposal of such sources.
In the pharmaceutical industry, similar monitoring techniques are used for the accurate determination of the weight of dispensed powder drugs or tablets in containers, such as blister packs.
Also, in the medical industry, similar monitoring techniques are used for the accurate determination of quantities of dressings in packs.
Further, in the food industry, similar monitoring techniques are used for the accurate determination of product presence and/or mass.
However, in all the present radiation absorption monitoring techniques, the resulting signal(s) produced by the sensor(s) due to the receipt thereby of the residual radiation which has not been absorbed by the product, is influenced by several operating parameters which can vary indeterminately during the monitoring process. Such variable operating parameters include, in the case of radiation absorption monitoring techniques, the acceleration voltage applied to the radiation generator, for example, an X-ray beam generator, the radiation beam current of the generator and, in the vast majority of cases, changes in the ambient temperature of the monitoring environment.
These variations in such operating parameters, as well as others, during the monitoring process result in inaccurate monitoring measurements, which is undesirable if the physical property of the product is to be determined accurately.
Generally, it is difficult to stabilise some or all of these parameters to a degree which is sufficient to provide the required accuracy of physical property monitoring.
Several solutions have been proposed to the problems associated with the monitoring of a property of a material. For example, Johnson, in his United State patent (U.S. Pat. No. 4,504,963), proposes a system for analysing meat in which a sample of meat is placed in a sample container which is irradiated with X-rays, the attenuated beam being detected and compared with a previously determined calibration. The signal of the attenuated beam is related to the fat content of the meat and thereby provides a measure of the fat content of the meat.
Hauni Mascinenbau AG in their European patent (EP0790006) propose an xe2x80x9con-linexe2x80x9d analysis method in which X-rays are utilised to monitor the density of a cigarette rod as it passes the apparatus. It is taught that an absolute measure of tobacco density nay be effected by continuously monitoring the dark signal of a detector element, the fill signal (un-attenuated beam) with a detector element, and the beam strength after passage through slices of the cigarette rod. The dark signal and fill signal are used to correct the readings of the other detector elements which monitor the beam through respective slices of the cigarette rod. In this fashion the apparatus provides an absolute measure of the density of tobacco.
Molins PLC, in their International patent application (WO 97/29654), disclose further apparatus for monitoring tobacco density in a cigarette rod in which a reference sample, a xe2x80x9cdummyxe2x80x9d cigarette, is irradiated with X-rays and the signal derived therefrom is used to control the X-ray emitter so as to ensure a constant output therefrom. By ensuring such constant output, the signal which is derived from the detector which measures the beam strength following passage of the X-rays through the cigarette rod is related to the density of the tobacco in the rod.
Accordingly, it is an object of the present invention to provide apparatus and an associated method, which overcomes, or at least substantially reduces, the disadvantages discussed above in relation to known radiation absorption techniques for monitoring a physical property of a manufactured product.
Thus, a first aspect of the invention resides in dual calibration apparatus for xe2x80x9con-linexe2x80x9d or continuous monitoring of a physical property of a material, such as the specific gravity of a processed meat product or the density, and hence weight, of tobacco in a cigarette rod, the apparatus comprising:
(a) means arranged to direct radiation into a material having a physical property to be monitored;
(b) first sensing means arranged to sense levels of residual measurement radiation passing from the irradiated material and to provide respective measurement signals representative of said sensed levels of residual measurement radiation;
(c) reference means which is arranged to be located in the path of the radiation, optionally adjacent or within the material whose physical property is to be monitored, and which has radiation absorption characteristics corresponding to predetermined low and high radiation absorption characteristics of the material whose physical property is to be monitored:
(d) second sensing means arranged to sense levels of residual reference radiation passing from said irradiated reference means and to provide reference signals representative of said sensed levels of residual reference radiation,
(e) means arranged to process the measurement and reference signals, to provide interpolated measurement signals; and
characterised in that, said reference means comprises a pair of spaced reference standards, a low radiation absorption characteristic standard whose absorption characteristic corresponds to a minimum level of the physical property to be monitored and a high radiation absorption characteristic standard whose absorption characteristic corresponds to a maximum level of the physical property to be monitored, the interpolated results being corrected to take into account any variable operating parameters of the apparatus and being representative of the actual monitored physical property.
In accordance with a second aspect of the invention, there is provided a method of xe2x80x9con-line-xe2x80x9d or continuous monitoring a physical property of a material, such as the specific gravity of a processed meat product or the density, and hence weight, of the tobacco in a cigarette rod, which method comprises;
directing radiation into a material having a physical property being monitored;
sensing levels of residual measurement radiation passing from the irradiated material;
providing measurement signals representative of said sensed levels of residual measurement radiation;
locating in the path of the radiation, optionally adjacent or within the material whose physical property is being monitored, reference means having radiation absorption characteristics corresponding to predetermined low and/or high radiation absorption characteristics of the material whose physical property is to be monitored;
sensing the level of residual reference radiation passing from said irradiated reference means;
providing reference signals representative of said sensed levels of residual reference radiation;
processing the measurement and reference signals to provide interpolated measurement signals; and
characterised in that, said reference means comprises a pair of spaced reference standards, a low radiation absorption characteristic standard whose absorption characteristic corresponds to a minimum level of the physical property to be monitored and a high radiation absorption characteristic standard whose absorption characteristic corresponds to a maximum level of the physical property to be monitored, and correcting the interpolated results to take into account any sensed variation of the operating parameters and thereby representing the actual monitored physical property.
In both aspects of the invention defined above, the radiation employed is preferably X-rays generated by a suitable X-ray source which, in the preferred embodiment to be described hereinbelow, provides a diverging X-ray beam directed at and into the material, as well as at and into the reference means.
Also, in the case of the inventive apparatus, the first sensing means for sensing levels of residual measurement radiation passing from the irradiated material and for providing measurement signals representative of those sensed residual measurement radiation levels, may be of any suitable form. In the preferred embodiment to be described hereinbelow, such first sensing means may comprise an X-ray detector capable of providing measurement signals representative of the residual measurement levels of X-rays received thereby from the irradiated material whose physical property is to be monitored.
Again, and in the case of the inventive apparatus defined above, the pair of spaced reference elements indicated above, may be of any suitable form, for example, an X-ray detector capable of providing reference signals representative of the levels of residual reference radiation received thereby.
The two spaced reference elements may each have its own second sensing means, possibly incorporated with the first sensing means, for example in a single array. In such a case, respective measurement and reference signals from all three sensing means can be processed, by suitable processing means, to provide interpolated measurement signals representative of the actual physical property of the material in question. In this manner, any operating parameters of the inventive apparatus, assembly and method which vary during the monitoring process and which can influence, in an undesirable manner, the sensed levels of residual measurement radiation from the material are xe2x80x9ccalibrated outxe2x80x9d using the reference signals, to provide a true value for the monitored physical property of the material.
At least insofar as the parameter of the material to be monitored is concerned, the radiation absorption characteristic of the material of the reference means such as the reference elements to be discussed hereinbelow, is preferably very close to or substantially the same as that of the material whose physical property is to be monitored.
Periodically, the pair of spaced reference elements, whose radiation absorption characteristics correspond respectively to predetermined low and high radiation absorption characteristics of the material whose physical property is to be or is being monitored, can be calibrated absolutely. For example, in the inventive monitoring apparatus, the radiation source and at least the second sensing means can be moved from the vicinity of the material chamber to a position where pre-certified calibration elements can be moved into the path of the radiation, for example, into the X-ray beam, between that source and the sensor means. Such calibration elements are certified to correspond to predetermined low and high percentage tolerance levels of the radiation absorption characteristics of the material in question and are used to calibrate out any medium or long term drift which may have occurred in the reference means located in the path of the radiation during the monitoring process. This arrangement may also be used to calibrate the linearity of the monitoring apparatus and assembly, particularly the signal processing means thereof.
Additionally or alternatively, such calibration may be facilitated by a series of certified references which can be indexed through the X-ray or other radiation beam by means of a motorised mechanism
Also, such calibration can be programmed to occur at predetermined time intervals.
Preferably, the geometry of at least those components of the inventive apparatus and assembly involved in the monitoring method is symmetrical or substantially so, in order to maintain uniform radiation of the sensing and reference means.
Further, it is to be understood that although X-ray radiation is preformed, other types of suitable radiation may be employed in the inventive apparatus, assembly and method described above.